0.25HP electric motor problems

[Bushbaby]

Hi All,
I've recent acquired a 0.25hp electric motor manufactured by the Small Electric Motors Ltd of Beckenham, Kent. It has a max speed of 1420rpm with a double pulley.

It does work and appears very smooth running for an old motor. It has one issue thought - when switched on, it will not start by its self put needs to be turned by hand. I've had a look at the wiring (! - not happy about some of the insulation tape thats been applied) but it doesn't have any form of cap which I assumed all AC motors need.

Can anyone help or guide here please??

Many thanks

Rob

[Joe]

It does sound like a lack of a starting capacitor but not ALL motors have them.

A bit more info and/or pictures would help.

- Joe

[Bushbaby]

Joe,
As requested, I've added some pics

Regards

Rob

           

[Yorkie]

Colin's your man for this - he used to work for Brookes in Huddersfield. It looks very similar to a motor that I had which Colin helped me with. It will have a 'start' winding' and a 'run' winding. I think that the 'start' winding draws a heavier current to give the motor a kick to start it spinning, then a centrifugal switch (which has little springs and a contact ring) swtiches the motor over to the 'run' winding. Could perhaps be that either the start winding is o/c or the centrifugal switch needs attention, as mine did. (I had to reverse the direction of my motor, and Colin was most helpful in advising me how to change over the windings to achieve that).

I'm sure Colin will see your post and will respond.

Best of luck with it Rob!

[Joe]

I think David's hit it on all counts. Col had trouble with a motor he was working on recently and the fault was the centrifugal switch. See http://golbornevintageradio.org/forum/sh...p?tid=1792

- Joe

[Retired]

Hi,

The following links might help a bit Rob;

http://community.ashworthcollege.edu/gro...g-problems

http://www.allaboutcircuits.com/vol_2/chpt_13/9.html

I'm having similar problems with the motor on my belt grinder; it won't self start but a tug on the drive belt gets it running.

I've already stripped it and cleaned the centrifugal switch but the problem remains. I think your motor will also have a centrifugal switch and this switch remains closed when the motor is at rest but once power is applied current flows through it to activate the "Start winding". The "Run" winding is permanently connected so at power up both windings are energized but once the motor comes up to speed the centrifugal switch clicks open dropping the start winding off line but the run winding remains energized hence the motor runs as normal.

I think it possible both our motors are suffering from open circuit start windings and a resistance check should confirm this. The start and run windings will have just two connections each; one to each end of the coil. It is easy to check continuity as each winding is identified a reading will be obtained; it's just a matter of taking a reading across the wires but all the wires will need disconnecting first to be sure. If the windings are good there should be a continuity reading across two pairs; if only one reading can be obtained across one pair then it's highly likely the start winding is open circuit and if the problem isn't something simple like a loose connection throw the motor away. Take a note of connections before disconnecting.

Before retirement I worked at Brook Motors here in Huddersfield for 24 years and must be one of the few guys in the country to physically handle well in excess of a million motors. These motors ranged from fractional horse power that could be lifted with one hand to motors weighing more than three tons. I was in logistics and at the height of production we were a central hub for our six factories. I lived and breathed electric motors and I couldn't switch off ; being in logistics we had to get all the motors out to our customers; the job was highly stressful and when I finally came down with shingles I saw the writing on the wall; get out before it kills me.

During all this time it was only natural that I picked up information and by being inquisitive I can now take a three phase motor; disconnect all six leads and re-connect in either Star or Delta by taking simple continuity checks. My big Startrite combination woodworking machine has three 3 phase 3HP motors fitted but with a bit of re-wiring and a pair of capacitors this machine has been running from single phase 240V for over ten years. One pair of capacitors runs all three motors as the motors are in-dependably switched allowing only one motor at a time to run.

I find such projects to be highly interesting but of course doing such work can be lethal to a novice so I'm never happy to divulge the techniques involved.

Kind regards, Col.

[Retired]

Hi,

Thanks David and Joe.

When I stripped my belt grinder motor and re-assembled all appeared well and the motor then started OK but has since returned to sulking and refusing to start so I think the problem is an open circuit start winding that is intermittent? It was cold in the garage when I stripped the motor so I just wanted to get the job done and my DMM was up in the workshop. It's not a big job to strip one of these motors. Being retired is a full time job with maximum overtime; I seldom seem to get time these days to play around with projects as other more pressing jobs keep popping up.

Fingers crossed Rob that it is a simple fault that you can easily sort out.

See you as planned at Rufforth Auto Jumble tomorrow morning David; I hope it isn't freezing.

It's time I got off my backside and crack on with the decorating.

Kind regards, Col.

[Bushbaby]

Many thanks Col et al.,
I shall indeed measure the continuity and report back

Regards

Rob

[Bushbaby]

Hi All,
Good news to report. I have now a working 0.25hp SEM Ltd motor up and running thanks to the invaluable help from my dear friend Col (Retired).

Now all I need to do is finish working on the Lathe (very slowly at the moment too!).

Rob

[Retired]

Hi,

You are most welcome Rob and I'm happy to have helped in some small way.

Although I worked at Brook Motors for 24 years I was involved in logistics so all my knowledge of the electrical side is self taught. As an apprentice mechanical engineer at the NCB I was on a six month training course at Crigglestone Colliery near Wakefield and I did so well that I completed the course early and was allowed to wander over to the apprentices in the electrical section; I was taught how to wire a 3 phase motor but apart from this I've picked up information as required over many years.

Modern six wire 3 phase motors are easy enough to sort out even if every connection is lost but a single phase motor that is old and been played around with is a totally different matter. Many have a centrifugal switch that drops the start winding offline once the motor reaches about three quarters full speed allowing the motor to induction run. However on an unknown single phase motor without circuit diagram the motor could be cap start/induction run or even cap start/cap run. A further problem with caps is trying to sort out the correct uF value.

As I explained to Rob the best place to start with an unknown single phase motor without circuit diagram is to disconnect all the wires after first marking them and drawing a sketch of the connections. Then take continuity readings on all the pairs of wires; with luck two pairs should give a reading these being the start and run windings; the start winding will have the highest resistance reading so these are marked "Start winding" the other pair with the lower resistance reading are marked "Run winding". I'm hopelessly colour blind so I simply arrange the connections to suit me but A1 is Live and A2 is Neutral. (Modern are U1 Live and U2 Neutral).

With the run winding wires connected directly to A1 & A2 supply these can then be ignored. The Start winding needs tracing through as the centrifugal switch needs connecting in "Series" with the winding then with the switch connected the two loose wires are connected to A1 & A2. At power up the run winding is energized and remains online whilst the power is on but the start winding becomes energized at power up only until the motor reaches about three quarters full speed then the centrifugal switch opens and drops the start winding offline allowing the motor to run on its run winding only. This is in very simple terms but is a good basis to work from.

I always find it difficult trying to help in offering advice to a friend some distance away using emails because with a motor on my bench I can experiment and see what I have got but I've seen many motors with other components attached; not only caps but heaters;thermistors; thermal protection; thermal detector; magnetic brake and reversing connections to name a few. Fortunately most of the small common old single phase motors are like Rob's with just the two windings and a centrifugal switch making them easy to sort out. If continuity cannot be found on two pairs of wires then I would assume the motor is not worth any further investigation and scrap it; these fractional horsepower motors are cheap and plentiful.

http://ecatalog.squared.com/pubs/Machine...CT9201.pdf

I'm certainly no expert on motors but I can usually get them running and just for interest please check out the above site; it's enough to put anyone off even looking at a motor.

It's time I cracked on with the decorating. Good luck with the lathe restoration Rob and I'm here if you think I can assist further; please keep me posted.

Kind regards, Col.